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SALTWATER INCURSION INTO MICRO TIDAL WETLANDS: CASE STUDIES FROM MATAGORDA, TEXAS AND HUMACAO, PUERTO RICO A Dissertation by RICARDO J. COLÓN Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Chair of Committee, Rusty A. Feagin Committee Members, Jason B. West Ben X. Wu Roél López Head of Department, David D. Baltensperger August 2013 Major Subject: Ecosystem Science and Management Copyright 2013 Ricardo J. Colón ABSTRACT Global climate change threatens the survival of microtidal wetlands by altering fundamental hydrological aspects such as precipitation patterns and tidal exchange. The combination of these stressors results in increased flooding period and soil salinity in coastal wetlands. In this study, we combined the use of detailed hydrological measurements (wetland water level and salinity), LIDAR elevation models, and water stable isotopes tracers (δD, δ18O) to study the balance between freshwater and saltwater inputs on two microtidal wetlands: a saltmarsh in Matagorda, Texas and a freshwater- forested wetland in Humacao, Puerto Rico. In Matagorda, Texas, we described the process of connectivity between different hydrologic units (isolated and connected ponds) within the saltmarsh. Pond connectivity only occurred when water levels in major water bodies adjacent to our study site reached a threshold elevation of 0.39 m. Connections events were correlated to rainfall and— to a lesser extent— wind speed and direction. We conclude that connectivity within the saltmarsh is driven by the combined effect of tidal influence and rainfall inputs, factors that will be altered by sea level rise and climate change-related changes in long term weather patterns. In Humacao, Puerto Rico, we gathered a detailed dataset of changes in salinity and water level in a freshwater forested wetland dominated by the endangered salt intolerant species Pterocarpus officinalis. In addition, we studied tree water use and ii identified important water sources to the wetland using stable isotope tracers. Firstly, we provide evidence that recent hydrological alterations have effectively transformed the system from mostly freshwater, to a saltwater wedge estuary. Salinity inputs travel via a tidal creek channel that allows the progression of a saltwater wedge to the inland parts of the forest. Our results suggest that inland progression of the saltwater wedge is influenced by amplitude of tidal exchange in the middle portions of the tidal creek and by extended dry periods in the headmost part of the tidal creek. Isotope data showed that surface standing water was influenced by tidal water sources during the dry season, although the spatial extent of this influence was constrained to areas of the forest that had been previously deforested. The isotopic content of groundwater samples taken at increasing distances from the tidal creek revealed that— although surface waters are dominated by freshwater inputs (rainfall and runoff) during the wet season— the influence of tidal water sources at soil depths greater than 60 cm persists throughout the year. Nonetheless, isotopic content of Pterocapus officinalis stem water samples suggest that tree water uptake is constrained to very shallow, unsaturated parts of the soil. We conclude from both case studies that the long term vulnerability of microtidal wetlands to climate change is determined by the interaction of increased annual variability of freshwater inputs along with a steady increase in mean sea levels, and aggravated by extreme climatic events. iii DEDICATION Para Violeta, nuestro sol brillante. iv ACKNOWLEDGEMENTS I owe a great deal of gratitude to my committee chair, Dr. Rusty A. Feagin, for his guidance and encouragement through every single step of this research. Dr. Feagin has not only supported me since we first met at Texas A&M University (TAMU), but has continued to do so over the years, allowing me the space to be creative while providing structure and direction to my professional development. Also, I thank my committee members, Dr. Jason B. West, Dr. Ben. X and Dr. Roel López for being excellent mentors and creating a positive experience. I would not have been able to complete my PhD education and research without the financial support of the Hispanic Leaders in Agriculture and the Environment (HLAE) program, the Alfred P. Sloan Foundation and the Department of Ecosystem Science and Management of Texas A&M University. I would also like to acknowledge the financial support of the Society of Wetland Scientists and the Mexican-American and Latino Research Center at different stages of the project. I would like to thank my senior mentors for the guidance. A special thanks to Dr. Manuel Piña, who consistently challenged me to become a leader in all aspects of my career and who encouraged me to expand my vision to the community that supported me in the first place. In addition, I thank Dr. Tom Boutton and Dr. David Briske for sharing their vast understanding of ecology with such clarity and simplicity that it was very easy to learn from them. v I thank my laboratory colleagues Frances Toledo, Amy Williams, Ranjani Wasantha Kulawardhana and Marie Cline for their inputs, and my HLAE fellows for sharing their insights, knowledge and experiences with me. A very special thanks to all my friends and colleagues from the Coastal Marine Biology program in the University of Puerto Rico at Humacao (UPR-H), they are an extremely brilliant group of scientists and I am fortunate to be part of that group. Establishing a research project in the Pterocarpus officinalis swamp of the Humacao Natural Reserve (HNR) was challenging due to lack of accessibility and normal swamp conditions of the field. In this context, I must first thank my wife, Dorimar Ortiz, for bravely going out of her comfort zone in our efforts to find the most appropriate entry point to the site. Because of her drive and creativity we were able to finally reach the swamp for the first time in January 2010, admire its magnificent landscape, and confirm our compromise to contribute to its conservation through our ecological research. Secondly, I must thank Rafael J. Benítez for his unconditional support in multiple stages of the project and for sharing equipment, effort, and knowledge without hesitation. I also thank Yoshua Cortés, Marangelly Torres, Doel Delgado and Dr. Richard McKenzie for their assistance on the field. At different points of my project I was fortunate enough to receive vital input from brilliant ecologists in Puerto Rico. For this, I thank Dr. Elvira Cuevas, Dr. Jorge Ortiz and Dr. Ariel Lugo for taking from their time to share their knowledge with me. I also thank Dr. Bill Gould for his support, and Ernesto Díaz and Kasey Jacobs from the vi Puerto Rico Climate Change Council for providing me with the opportunity to collaborate with their efforts. Also, I thank Manuel Córbet from the Humacao Natural Reserve for supporting our research and providing vital information for our project. I owe a very special thanks to UPR-H undergraduate colleagues Alejandro Santana, Natalia B. López and Carlos M. Zayas, with whom I collaborated closely for three years. I began my collaboration with these students in an effort to increase ecological research activities in the HNR and to show the potential of graduate-mentored initiatives to increase undergraduate participation in research activities. These students are not only extremely creative, smart, and hard-working, but also took their participation in the group beyond our expectations, and for the most part, made the most important efforts in the field possible. This project could not have been possible without them. In this context I would like to thank all the UPR-H faculty members that at some point or another supported me and these students in our collaboration: Dr. Denny S. Fernández, Dr. Deborah Parrilla, Prof. Cedar I. Garcia, Dr. Miguel P. Sastre, Prof. Silvia Velez, Dr. Neftalí García, Dr. Edgardo Ortiz, and Dr. Francisco Fuentes. I would also like to thank Luis Villanueva from Purdue’s Soundscape Ecology Laboratory for his quick replies to our questions about soundscape ecology research methods and for making these methods easily accessible to the public. Also, I thank Dr. Cheryl L. Dybas and Dr. Wilson González-Espada for taking interest in our projects and sharing them with the public. vii The Strategies for the Education of Ecology and Diversity and Sustainability (SEEDS) program of the Ecological Society of America (ESA) has consistently provided me support and professional growth opportunities. In particular, I would like to extend my profound gratitude to Melissa Armstrong, whose encouragement and support has help many ecology students, including myself, achieve their goals. The SEEDS program has also been instrumental in the expansion of my academic interests to areas outside wetland ecology. I thank all my SEEDS colleagues for sharing their views of the discipline and providing me with fertile opportunities of collaboration within the organization. In addition, I thank all of the people at the ESA and funding organizations that make the SEEDS program possible. Finally, I must thank my family for making everything possible. My parents, Raúl Colón, who me taught me to constantly seek knowledge on my own, and Lucía Rivera, who taught me the incredible value of persistence. Their values, love and support made me the person I am today. Equally important has been the unconditional love of my brothers, Carlos M. Colón and Juan R. Colón, who were my first mentors and believed in me more than anyone. My wife, Dorimar Ortiz, had an integral role during all the stages of my PhD preparation. She contributed in the field and in the revision of manuscripts, patiently supported me through the vicissitudes of graduate school, and took more than her share of household and parenting chores, all so I could complete my work.

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